The present invention relates to disk circuits and more particularly to a method and apparatus for reading information from a magnetic disk by biasing a read head.
Conventional magnetic storage devices include magnetic transducer or xe2x80x9cheadxe2x80x9d suspended in close proximity to a recording medium, for example a magnetic disk, having a plurality of concentric tracks. The transducer is supported by an air-bearing slider mounted to a flexible suspension. The suspension, in turn, is attached to a positioning actuator. During normal read operation, relative motion is provided between the head and the recording medium as the actuator dynamically positions the head over the desired track. The relative movement provides an airflow along the surface of the slider facing the medium, creating a lifting force. The lifting force is counterbalanced by a predetermined suspension force so that the slider is supported on a cushion of air. Airflow enters the leading end of the slider and exits from the trailing head. This air is used to prevent the head from contacting the disk, which would result in damage.
Writing data is typically performed by applying a current to the sensor or the head so that a magnetic field is induced and an adjacent magnetic-permeable core, with the core transmitting a magnetic signal across any spacing and protective coating of the disk to magnetize a small pattern or digital bit of the medium within the disk.
Reading of the information in the disk is performed by sensing a change in magnetic field of the core as the transducer passes over bits in the disk. The changing magnetic field induces a voltage or current in the inductive coupled coil. Alternatively, reading of the information may be accomplished by employing a magneto-resistive (MR) sensor, which has a resistance that varies as a function of the magnetic field adjacent to the sensor. In order to increase the amplitude and resolution of the reading bits, the MR sensor is typically positioned on the slider as close to the disk as possible. Connected to these heads are sensors are read circuits which amplify the recorded data and eliminate noise.
However, recently, some of the manufacturers of these MR sensors have switched from MR heads, which employ a constant current source to MR heads, which employ a constant voltage source. Thus, there is a need for a read circuit, which provides a constant voltage source. Recently, the hard disk drive (HDD) industry has been moving toward high resistance heads on the order of between 50 and 150 ohm read heads. Previous pre-amp circuit designs were insufficient for these high resistance heads due to poor common mode rejection (CMRR), noise, voltage bias loop instability and poor switching performance. Thus, there is a need for a circuit to improve the CMRR, noise switching, and stabilized loop bias for these high resistance heads.
FIG. 1 illustrates a waveform diagram.
The present invention provides a pre-amp circuit that can be used for high resistance read heads. More particularly, the pre-amp circuit of the present invention eliminates and reduces the problems associated with common mode rejection.
The present invention allows high resistance in the emitter of specific transistors by matching the emitter resistances to be approximately equal. This matching of resistances improves the common mode rejection.